The present invention relates to a detection system for detecting a frequency of a power supply voltage and, more particularly, to a power frequency detection circuit in a signal transmission system which utilizes the building or house wiring.
A signal transmission system has been developed, which utilizes the building or house wiring as a data transmission line. In such a signal transmission system, the power frequency is often used as a reference clock. To achieve an accurate operation, the power frequency component must be correctly detected without regard to the noises.
Accordingly, an object of the present invention is to provide a detection system for detecting a frequency component of a power voltage.
Another object of the present invention is to provide a power frequency detection system for use in a signal transmission system which utilizes the building or house wiring as a data transmission line.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, a zero-crossing detection circuit is provided for detecting the frequency component of the power voltage applied thereto. An inhibition system is provided for precluding the generation of an output from the zero-crossing detection circuit for a preselected period of time after the zero-crossing detection circuit has developed the previous detection output. The inhibition system minimizes an erroneous operation of the zero-crossing detection circuit as the zero-crossing detection circuit will not recognize any noise as the power frequency component as long as any noise occurs within the system while the zero-crossing detection circuit is placed in an inoperative condition by the inhibition system.